Conventional magnetic heads typically employ lapping to fabricate structures within the head. For example, lapping is typically used in processing a write transducer. More specifically, after pole formation, lapping may be used to remove a portion of the device to expose the air bearing surface (ABS). Lapping determines the windage, or the length measured from the ABS to the flare point of the pole of the write transducer. Similarly, lapping may be used in fabricating other structures in a head, such as the read sensor of a conventional read transducer. The dimensions of the pole and components of the read sensor can have a large effect on their performance. As such, precise control of the lapping process can be important.
In order to control lapping an electronic lapping guide (ELG) is typically used. The conventional ELG is essentially a resistive stripe coupled with leads that are used to determine the resistance of the conventional ELG. The conventional ELG has a preselected length from the surface being lapped. As lapping continues, the surface is worn away, and the length of the conventional ELG decreases, along with the resistance. Conventional ELGs are described in further detail in U.S. Pat. No. 8,151,441, entitled, “Method for providing and utilizing an electronic lapping guide in a magnetic recording transducer”, the entire content of which is incorporated herein by reference.
In some related art designs, a writer ELG (WELG) is built at the bottom of a writer pole. Locating the WELG at the bottom of the writer pole has process friendly benefits that include avoiding the changes and variations from the pole fabrication process. However, such WELG placement does not simulate the pole process variation effectively and has a relatively large sigma because of side wall variations.
With the magnetic area density dramatically increasing for modern designs, the size of the writer pole is getting smaller and smaller. The yield loss on such high area density magnetic heads is mainly caused by deficiencies in magnetic write width (MWW). As such, it would be desirable to reduce MWW sigma to improve overall yield and reduce the manufacture costs.